This invention relates generally to radio-frequency (xe2x80x9cRFxe2x80x9d) powered medical apparatus and ablation of biological tissues. More particularly, this invention concerns catheter-based RF antenna for ablating biological tissues within the body vessel of a patient and for the treatment of cardiac arrhythmias.
In recent years medical devices have gained significant acceptance in the medical community as an important treatment modality for heart diseases and other serious ailments, which were traditionally remedied by medication or surgical operation. Two fundamental trends have emerged in the treatment of cardiac diseases. The first has been the shift from open-heart surgical procedures to less invasive and less expensive catheter-based treatments, which are safer and less debilitating.
The second trend is represented by the shift from the use of anti-arrhythmic drugs to minimally invasive catheters or other device-based therapies to palliate incurable arrhythmias. For example, automatic cardioverter-defibrillator are routinely implanted in patients with lethal ventricular arrhythmias to reduce the likelihood of sudden death. Thus, radio-frequency (RFxe2x80x9d) catheter ablation is now being performed in large number of patients suffering from cardiac arrhythmias.
Despite these advances in technology, atrial fibrillation (xe2x80x9cAFxe2x80x9d) remains a significant challenge. AF, a rapid irregular rhythm in the atria or upper chambers of the heart induced by non-uniformed electrical pulses, represents a leading cause of stroke and heart attack and a major health care burden. To date, the most effective surgical procedure for the treatment of AF has been the Maze procedure undertaken in xe2x80x9copen-heartxe2x80x9d surgery. In the Maze procedure, incisions are made along pre-determined lines exterior of the atrium, which are then sutured together. As healing develops, scars are formed along the incision lines thereby forming barriers to the conduction of electrical impulses. By creating such barriers, AF can no longer be sustained and regular heart rhythm is restored. However, the Maze procedure has not been widely adopted due to the morbidity and mortality associated with open-heart surgery, which involves the opening of the chest cavity and cutting of the chest bones.
One new approach to mimic the Maze operation is represented by catheter-based radio-frequency ablation technique, wherein, instead of surgical incisions, a catheter-electrode is applied to destroy or ablate the heart tissues inside the atrial chamber. The catheter-electrode is passed through the artery for access to the atrium, as commonly practiced in the medical field. Within the atrium, the tip of the catheter-electrode is positioned, usually with the aid of x-ray or fluoroscopic means, and is brought into contact with the heart tissue at a desired location or spot where ablation is required. At this spot, the tissue is destroyed by resistive heating generated from the catheter-electrode. Thereafter, the catheter-electrode is re-positioned to the next spot for ablation. A series of spot ablations thus mimics the lineal lesions as accomplished under the Maze procedure against the conduction of electrical impulses.
Existing catheter-based ablation procedures are recognizably less intrusive than xe2x80x9copen-heartxe2x80x9d surgery. In addition, during the ablation, disruption of cardiovascular function is reduced. However, a successful catheter-based radio-frequency ablation procedure requires the ablation of tissue spots within the spatial or proximity tolerance between adjacent spots, usually less than 2 millimeters, to prevent the passage of electrical impulses. In that connection, the task for the precise placement of the catheter-electrode represents a critical element of a successful procedure.
A major drawback of such existing procedures is in the time-consuming task in positioning the catheter-electrode at the desired ablation spots within the atrium while the heart chamber muscles are pulsating. Movements of atrial wall or the heart muscles often render accurate placement of the catheter-electrode difficult, and slippage of the catheter-electrode tends to occur thereby damaging portions of the atrium where ablation is not desired. As a result, placement of the catheter based RF ablation cannot be efficiently accomplished, and prolonged procedure time, in excess of 12 hours, can be expected. Further, during the procedure, x-ray or other irradiating means are routinely employed for locating and positioning the catheter-electrode, which dictates the use of heavy lead protective gear by the electro-physiologist. As a result, such inconvenience is often amplified by the prolonged procedure time, which detracts from the use of catheter-based electrode as an efficient means for tissue ablation.
To minimize the risk of slippage, for example, in U.S. Pat. No. 5,741,249, a catheter-based microwave antenna is disclosed wherein a distal tip is incorporated into the antenna to anchor it to the atrial wall. However, while this design reduces the likelihood of antenna or catheter-electrode slippage during each ablation step, it does not eliminate the consuming task to secure precise placement of the antenna along the desired ablation path for each ablation step. Thus after each ablation step, the antenna has to be re-positioned and anchored precisely at the next spot which must be located within the spatial or proximity tolerance on the ablation path as referenced above.
Accordingly, effective treatments for atrial fibrillation with catheter ablation will require the creation of long or overlapping lineal or curvilineal ablation lesions on the inner surface of the atrium. These lesions can then act as barriers to the conduction of electrical impulses, thus preventing atrial fibrillation.
It is also recognized that a critical requirement for the effective catheter-based ablation of atrial fibrillation is the ability to stabilize and anchor the catheter and microwave antenna inside the atrial chambers. New catheter ablation systems, preferably capable of producing long or overlapping lineal or curvilineal ablation lesions, are required for the development of minimally invasive catheter-based curative procedures for atrial fibrillation.
The present invention provides a design of such a catheter system, which can be used not only for atrial fibrillation but for ablation of biological tissues in other body vessels. The catheter system contains stabilizing and anchoring mechanisms employing monorail and looped antenna guide, sensors for monitoring different parameters during ablation, and handle with control slides for easy steering and manipulation of the catheters.
According to the present invention, an improved radio-frequency catheter system is provided for ablating biological tissues of a body vessel, including the atrium of a patient. The catheter system comprises a catheter that is adaptable for insertion into the body vessel and a deployable antenna guide disposed within the catheter lumen. A deployable radio-frequency antenna, together with a hollow co-axial cable, is provided at the distal portion of the catheter to receive and transmit radio-frequency energy for tissue ablation. In a representative embodiment of the invention, the antenna includes a helical coil and has an axial passageway to accommodate the antenna guide, which, upon deployment prescribes the ablation pathway of the antenna for tissue ablation. The antenna guide includes elongated portions which are secured to control slides for positioning and deployment control. The antenna guide is deployable within a body vessel to form a loop configuration that is conformable to the contour of the body vessel. Alignment of the loop with the desired tissue ablation pathway is facilitated with the use of radio-opaque markers and intracardiac electrodes mounted along the antenna guide. After the loop is formed within the body vessel, the radio-frequency antenna will be deployed along the antenna guide for tissue ablation.
In an alternate embodiment of the present invention, one of the elongated portions of the antenna guide is secured to a positioning control slide, and the other portion is secured to the distal portion of the catheter. As a further alternate embodiment of the invention, the antenna guide is formed as an elongated flexible member having a detached distal end portion that is terminated with a distal tip.
The radio-frequency catheter system of the present invention can also incorporate various alternate radio-frequency antenna designs. In one such alternate embodiment of the present invention, the radio-frequency antenna comprises a monopole bead disposed at the distal portion of the catheter for delivering an optimal radiation pattern while minimizing refection and voltage standing wave ratios. In another alternate embodiment of the present invention, a microstrip flexcircuit is provided.
In application, the antenna guide is deployed out of the catheter lumen to establish contact with the interior surface of the body vessel. The flexibility of the antenna guide enables it to flex to conform to the contour of the body vessel to define the ablation pathway for the radio-frequency antenna.
The present invention effectively reduces if not avoids the need for repetitive pin-point precision placement of the ablation catheter electrode of the prior art. The present invention conveniently places the radio-frequency antenna along the locus of an antenna guide which defines the tissue ablation pathway. At the same time, the present invention ensures a continuous ablation pathway and substantially reduces the risk of electrical impulse leakage between ablated spots of the prior art. Accordingly, the present invention substantially accomplishes the objective of the Maze procedure in achieving curvilineal lesions yet without the need for open-heart surgery. These and other aspects and advantages of the invention will become apparent from the following detailed description, and the accompanying drawings, which illustrate by way of example the features of the invention.